Now as a business, I disagree to some extent. You are absolutely correct in your last two statements about the overall size and growth potential of the "hobby" carPC market. It's not going to change, other than gradually shrink as auto makers start to include all the stuff we like straight from the factory. But as I pointed out before, I actually do make money in the carPC business, and if I chose to do it full-time, could probably make a pretty nice living at it. It's most definitely a "niche" market, but I think there are a number of niches available that haven't been fully explored and which could be quite profitable for the right entrepreneur. Race and rally systems, public service/safety systems in small or rural communities. The previously mentioned show and exotic car systems. And all of these ideas work pretty well as a regional business model, meaning that the national market can probably support several moderately-sized players.
But I guess we'll see, won't we? The next couple of years should tell the tale of what this hobby (and the businesses that surround it) will look like.